The July issue of the Archives of Neurology reported a longitudinal study of more than 3,000 subjects in which a link between vitamin D and Parkinson’s disease was found. In the 29-year follow-up period, there were 50 incident cases of Parkinson's disease. The study was carried out in Finland where there is restricted sunlight exposure. It is a population that typically has low vitamin D levels. The mean serum level was about 50% of the suggested optimal level of 75 to 80 nmol/L.
The investigators found that individuals with a serum vitamin D concentration of at least 50 nmol/L had a 65% lower risk for Parkinson's than those with values less than 25 nmol/L after adjustment for several potential confounders. The relative risk between the highest and lowest vitamin D levels was 0.35.
Vitamin D is no longer considered a vitamin, but rather a hormone that has autocrine and paracrine functions well beyond those of regulating calcium absorption and bone health.
The exact mechanisms by which vitamin D may protect against Parkinson's disease are not fully understood. Vitamin D has, however, been shown to exhibit neuroprotective effects through antioxidative mechanisms, neuronal calcium regulation, immunomodulation, enhanced nerve conduction, and detoxification mechanisms.
The association with and possible causal role of insufficient vitamin D in many chronic diseases, such as Multiple Sclerosis, is becoming more widely appreciated yet what constitutes an optimal blood concentration of vitamin D for humans, and specifically for the human nervous system, remains unknown.